Sperm binding to the zona pellucida of the unfertilized egg is not strictly species specific because heterologous binding between gametes occurs. To study the sperm's role in sperm-egg interaction monoclonal antibodies were prepared toward mouse sperm surface antigens. Four hybridoma cell lines were isolated that produced monoclonal antibodies (MCA) to mouse sperm surface antigens. The MCA were tissue and species specific and were targeted against integral sperm antigens. Furthermore, the antigens were localized in distinct domains of the mouse sperm, specifically: acrosomal cap, mid-piece and tail, in contrast with polyclonal antibodies which were localized on the entire sperm surface. Sperm binding to the zona pellucida was inhibited by tail and acrosome directed antibody and tail directed antibody immobilized sperm. To study the egg's role in sperm-egg interaction antibody was made against zona pellucida. Initial results on active immunization of female monkeys with porcine zona pellucida indicate that they produce anti-zona antibody and they failed to conceive when mating was started after the maximal levels of serum titer was reached. The anti-sperm will be used to investigate the ovum aspect of sperm-egg recognition.